The officer can be heard repeatedly shouting “get on the ground” before a gunshot rings out. Both men are black.

Thomas’ family urged local politicians at a Houston City Council meeting to act over “police brutality”.

His sister Kita Thomas-Smith told the Houston Chronicle: “It feels like premeditated murder. He was clearly walking, not running, towards the deputy, not trying to hurt or harm him.”

She said her brother had been suffering from depression after the deaths of his two children in 2016 but had not been diagnosed with a mental illness, his family said.

Harris County deputy Brewer, who had a Taser with him but did not fire it, has been placed on leave as homicide detectives and prosecutors investigate the shooting.

In a statement, Houston police said that Thomas had been “walking in the middle of the intersection” of a road with his trousers around his ankles, “talking to himself and hitting vehicles as they passed by”.

The footage shows a driver confronting and pushing Thomas.

“The deputy exited his vehicle to stop the altercation, at which time the suspect started walking toward him,” the force said. “The deputy gave Thomas verbal commands to stop, which he ignored and continued to advance toward the deputy. Fearing for his safety, the deputy discharged his duty weapon, striking Thomas once in the chest.”

Thomas was taken to hospital, where he was pronounced dead.

Harris County Sheriff’s Office said Thomas appeared to have had “some object” in his hand, but no weapon was recovered and footage shows he was not carrying anything.

A tearful Ms Thomas-Smith told councillors: “I’m speaking on behalf of police brutality. My brother was not armed, not trying to harm and possibly, he just wanted someone to help him.”

Thomas’ wife has been charged with murder trial after allegedly drowning their two children, aged five and seven, in the bath.

Mayor Sylvester Turner told Ms Thomas-Smith: “I certainly feel your pain. We are certainly sorry for any life that is taken.”

He stressed the need for police training, while Harris County sheriff Ed Gonzalez said his department would review its use-of-force policy.

Thomas’ killing was condemned by the Texas branch of the American Civil Liberties Union.

“It’s difficult to imagine how this shooting could possibly be justified,” said Sharon Watkins-Jones, its director of political strategies. “We must demand that our law enforcement agencies, who are sworn to protect our communities, be held accountable whenever deadly force is used unlawfully.

“But whatever the excuse, another unarmed black man has been killed by law enforcement, in the street and in broad daylight, and the only reason we know about it is because of bystander footage.”